Showing papers on "Alloy published in 1973"

Morphology of y’ and y” precipitates and thermal stability of inconel 718 type alloys

Abstract: The precipitation of the γ’ (Ll2) and γ" (DO22) phases has been studied in four alloys Fe-Ni-Cr-Ti-Al-Nb containing a higher Ti + Al/Nb ratio than that of the INCONEL 718 alloy. For these alloys, the precipitation microstructure varies rapidly with aging temperature and composition. Bct γ"particles have always been found to precipitate on γ’ phase. Moreover, by aging three alloys above a critical temperature, a “compact ntorphology” has been observed: cube-shaped γ’ particles coated on their six faces with a shell of γ" precipitate. This microstructure has proved to be very stable on prolonged aging. A thermal stability better than that encountered in nominal INCONEL 718 alloy can thus be achieved. The influence of composition and aging temperature on the conditions that bring about this “compact morphology” has been investigated. A minimal Ti + Al/Nb ratio between 0.9 and 1 has been determined, allowing the “compact morphology” to be obtained.

Mechanisms for the hot corrosion of nickel-base alloys

Abstract: The Na2SO4-induced accelerated oxidation of nickel-base alloys containing elements such as Cr, Al, Mo, W, and V has been studied in 1.0 atm O2 in the temperature range of 650° to 1000°C. It has been found that the hot corrosion behavior of these alloys can usually be characterized according to one of two types of attack: 1) Na2SO4-induced accelerated oxidation; 2) Na2SO4-induced catastrophic oxidation. In both types of hot corrosion, accelerated oxidation occurs as a result of the formation of a liquid flux based on Na2SC>4 which dissolves the normally protective oxide scales. Catastrophic, or self-sustaining rapid oxidation can occur in alloys which contain Mo, W, or V, because solutions of oxides of these elements with Na2SO4 decrease the oxide ion activity of the molten salts, producing melts which are acidic fluxes for oxide scales. The accelerated oxidation type of attack which was observed with most alloys which did not contain Mo, W, or V, was more severe than for normal oxidation, but much less severe than catastrophic oxidation. Na2SO4-induced accelerated oxidation occurs because the oxide ion activity of the Na2SO4 increases to the point where oxide scales can partially dissolve in the basic melt. Generally, this basic fluxing results from the diffusion of sulfur from the Na2SO4 into the alloy. In some alloys, the formation of sulfides during basic fluxing is a sufficient condition to cause accelerated oxidation. In other alloys, changes in the oxidation mechanism occur because of depletion of the alloy surface, concomitant with basic fluxing, of those elements needed for protective oxide scales, such as aluminum and chromium.

An FIM-atom probe study of the precipitation of copper from lron-1.4 at. pct copper. Part II: Atom probe analyses

Abstract: Chemical analyses of individual precipitates found during the initial stages of precipitation of copper from Fe-1.4 at. pct Cu at 500°C were made with the FIM-atom probe. Precipitates as small as 8 × l0−8cm in diam were analyzed. The results indicate that the precipitate nuclei contain much less copper than the equilibrium e phase and that most of the particle-matrix boundaries are less than 10−7 cm wide. The average copper content of the precipitates increases with aging time until well after the alloy reaches its peak strength. Thermodynamic calculations show that it is reasonable to expect the precipitate compositions that were experimentally observed.

Tracer diffusion of59Fe and51Cr in Fe-17 Wt Pet Cr-12 Wt Pet Ni austenitic alloy

Abstract: The volume and grain-boundary diffusion of59Fe and51Cr have been studied in an austenitic iron alloy containing 17 wt pct Cr and 12 wt pct Ni. The diffusivities in this alloy of these two tracers and63Ni are compared with their diffusivities in pure iron and in other austenitic stainless steels. For volume diffusion at any particular temperature in the present alloy, Cr is the most rapid while Ni is the slowest, and all three tracers diffuse slower than that reported for pure iron or for other austenitic stainless steels. For grain-boundary transport, Fe diffuses most rapidly above 850°C and Ni diffuses most rapidly below that temperature. The activation energies for both volume and grain-bounary diffusion obey the relationshipQ Ni

Reducing the susceptibility of alloys, particularly aluminium alloys, to stress corrosion cracking

Abstract: A method is described of thermally treating the 7,000 series aluminum alloys that have been subjected to a solution heat treatment at a high temperature and then to an ageing treatment at a lower temperature, thereby hardening the alloy but likewise producing therein a susceptibility to stress-corrosion cracking. The novel method comprises the steps of (1) subjecting the alloy to a retrogression heat treatment for a short period of time at a temperature above the age-hardening temperature of the alloy but below the solution heat treatment temperature, and (2) subsequently subjecting the alloy to a re-ageing heat treatment for a substantially longer period of time at the age-hardening temperature of the alloy. This method substantially reduces the susceptibility of the alloy to stress-corrosion cracking while retaining its original strength.

The formation and structure of precipitates in a dilute magnesium-neodymium alloy

Abstract: The precipitation behaviour of a binary Mg-0.5 at.% Nd alloy has been studied by electrical resistivity and electron microscope techniques. A general scheme of precipitation is proposed, and the conditions defined under which each phase precipitates. G.P. zones are shown to exist, their formation being dependent on the quenched-in vacancy population as in aluminium alloys; in addition, there are two further non-equilibrium phases, and the equilibrium precipitate. The morphology and structure of each of these phases has been investigated, and related to the good elevated temperature strength shown by this alloy.

Composition and methods for preparing liquid-solid alloys for casting and casting methods employing the liquid-solid alloys

Abstract: A metal composition characterized by degenerate dendritic or nodular primary discrete solid particles suspended in a secondary phase having a lower melting point than the primary particles and which secondary phase can be solid or liquid. The method involves raising the temperature of a metal alloy to a value at which the alloy is largely or completely in the molten state. The melt then is subjected to vigorous agitation and the temperature is reduced to increase the portion of the mixture in solid degenerate dendrite or nodular form up to about sixty-five percent, but usually up to about fifty percent, while continuing the agitation. At this juncture the temperature of the liquid-solid composition can be reduced to cause solidification thereof or it can be cast. The solidified composition can be stored and later it can be brought again to the liquid-solid mixture state and then recast.

Thermodynamic properties of solid alloys of chromium with nickel and iron

Abstract: The thermodynamic properties of chromium have been determined in the Ni-Cr and Fe-Cr binary systems and in the Fe-corner of the Fe-Ni-Cr system. These properties are based on experimental measurements using solid oxide electrolyte cells of the type: Cr, Cr2O3 I ThO2-Y2O3Cr (alloy), Cr2O3. In the Ni-Cr system, between 900 and 1300°, the activity of chromium exhibits negative deviation from ideality up to about 25 at. pct chromium. For alloys higher in chromium content, the activity of chromium exhibits positive deviation from ideality. In the Fe-Cr system, between 900 and 1200°, and 0 and 63 at. pct Cr, the chromium activity when referred to solid pure chromium exhibits positive deviation from ideality in both the γ and α phases, approaching ideality with increasing temperature. The nickel and iron activities in these two respective binary systems were calculated by a Gibbs-Duhem integration. The activity of chromium, referred to solid pure chromium, was measured between 900 and 1200° in solid Fe-Ni-Cr alloys with chromium concentrations of 9, 20, and 30 at. pct and Ni concentrations of 8, 18, and 30 at. pct. Additions of nickel to Fe-Cr alloys in the above concentration range are found to increase the chromium activity. The effect of nickel in increasing the chromium activity is greater at both greater chromium contents and lower temperatures.

Diffusion of hydrogen in titanium alloys due to composition, temperature, and stress gradients

Abstract: A theoretical and experimental study was conducted to determine the combined effects on interstitial diffusion in metals of gradients in interstitial concentration, in solvent composition, in stress, and in temperature. The theory consolidates relationships, some of which have been previously published. It is based on macroscopic irreversible thermodynamics, and is applicable to anisotropic or Isotropic materials. Experiments were conducted and literature analyzed to determine the numerical quantities required to predict the change in hydrogen distribution with time for pure and alloy titanium, where the solvent gradient, stress gradient, and temperature gradient are constant with time. The diffusion driving forces for solute gradient, solvent gradient, and stress gradient are related to the effect of each factor on hydrogen activity. In addition, the material property which determines the diffusion driving force of a stress gradient for anisotropic material is a matter tensor analogous to the scalar partial molal volume used for isotropic material. The experiments, conducted with commercially pure titanium and titanium alloy, 6A1-4V, consist of measuring the effect of alloy additions and stress on the hydrogen activity in solid solution and the dilatation effect of hydrogen. Stress states tested were tension, compression, and torsion. The measurements were made by exposing titanium and the alloy to hydrogen at temperatures from 600° to 800° C, and measuring the equilibrium hydrogen gas pressure at various solid solution hydrogen contents. Both materials were tested with and without stress. Tension decreased the activity, compression increased it, and torsion had no effect. This is consistent with the stress effect theory of Li, Oriani, and Darken. The stress effect corresponds to an apparent partial molal volume of 1.7 to 2.2 cm3/mol, depending on the alloy and hydrogen content.

Thermomechanical Treatments on High Strength Al-Zn-Mg(-Cu) Alloys

Abstract: An investigation was carried out to determine the metallurgical properties of Al-Zn-Mg and Al-Zn-Mg-Cu alloy products processed according to newly developed Final Thermomechanical Treatments (FTMT) of T-AHA type. The results show that these cycles can be utilized to produce wrought products of high purity Al-Zn-Mg(-Cu) alloys characterized by equivalent toughness and ductility and much higher strength than conventionally processed commercial purity materials. Based on transmission electron microscopy studies, it was found that such improved behavior of FTMT material is attributable to the superposition of hardening effects, from aging precipitation and from dislocations. Preliminary stress-corrosion and fatigue tests indicate that these properties are not substantially influenced by T-AHA thermomechanical process. Further work is needed in this area, in order to better understand the directions to follow for developing better alloys.

Procedures and Precautions in Machining Titanium Alloys

Abstract: Titanium alloys have unique machining properties. While the cutting forces are only slightly higher than in machining steels, there are other characteristics that make these alloys more difficult to machine than steels of equivalent hardnesses. For example, the chip-tool contact area in turning a titanium alloy is only about one-third to one-half as great as that for turning a steel. Also, the thermal conductivity of titanium alloys is about one-sixth of that of steels. This combination of a small contact area and the low thermal conductivity results in very high cutting temperatures. At a cutting speed of 100 ft. /min., the temperature developed at the cutting edge of a carbide tool is 1000oF when cutting a steel, while on the titanium alloy, the temperature reaches 1300oF. Hence, the cutting speeds on titanium alloys must be lower in order to maintain a tool-chip temperature below that which results in short tool life.

Constitution of ternary titanium-tungsten-carbon alloys☆

Abstract: The ternary alloy system Ti-W-C was investigated by means of melting point, differential-thermoanalytical, X-ray diffraction, and metallographic techniques on hot-pressed and heat-treated, as well as melted, alloy specimens and a phase diagram from 1500 °C through the melting range established. Above 2530 °C, titanium monocarbide and the isomorphous cubic high temperature phase in the W-C binary system are completely miscible and the solid solution has a congruent (maximum-type) melting point of 3130 °C at the approximate composition (Ti0.54W0.44)C0.75. Below 2530 °C, the tungsten exchange in the cubic monocarbide is temperature-dependent and decreases to about 50 at.% at 1400 °C. The titanium exchange in W2C is less than 3 at.% at 1500 °C and reaches a maximum of 8 at.% at 2680 °C. In addition to the ternary congruent melting point, four reaction isotherms occur in the system: Two are pseudobinary eutectics, monocarbide + graphite at 3030 °C, and monocarbide + tungsten-rich metal alloy at 2700 °C; peritectic melting of the binary WC results in a class II reaction L + C⇄cubic monocarbide + WC(hex) at 2760 °C, and a fourth isotherm at 2680 °C is associated with a ternary eutectic between metal, monocarbide (B1), and W2C. Pseudobinary eutectic melting between the monocarbide and the metal phase is directly attributable to the large stability difference between titanium and tungsten carbide, and the measured tie line distribution in the two-phase range metal + monocarbide is in accordance with estimates from known thermodynamic values for the binary boundary phases. The phase behavior in pseudobinary monocarbide solutions is largely determined by the relative lattice size of the boundary carbides, except for systems (M, W)C1 − x (M = Ti, Zr, Hf, V). which show extra stabilization due to bonding effects.

Diamond particle having a composite coating of titanium and a metal layer

Abstract: A diamond particle of the MD or the SD type having a composite coating comprising a thin continuous layer of titanium adjacent the diamond surface and a metal layer on the titanium layer, the metal of the metal layer being capable of forming an alloy with titanium under the influence of heat and the titanium/diamond interface being essentially free of chemical bond formation. The invention further provides a method of making a metal bonded abrasive device which includes the steps mixing the above described particles with a suitable metal matrix, heating the mixture to a temperature exceeding 500*C, maintaining the mixture at the elevated temperature for a period of from 10 to 30 minutes, and allowing the mixture to return to ambient conditions.

The role of yttrium in high-temperature oxidation behavior of Ni-Cr-Al alloys

Abstract: Oxidation of five nickel-chromium-aluminum alloys with yttrium additions of between 0.005 and 0.7wt.% has been studied in the temperature range 800–1200°C in oxygen at pressures of 1, 10, and 720 Torr. The yttrium additions improve the oxidation behavior of the nickel-chromium-aluminum alloys, and generally an addition of 0.1 or 0.2 wt.% yttrium gives the best improvement in the oxidation resistance. In this case, the oxidation kinetics indicate asymptotic approach toward zero scale growth with time. This is suggested to be caused by the formation of subgrains in the alloy which (a) provide enhanced diffusion of aluminum to the surface and (b) increase the number of oxide nucleation sites. Preferred oxidation of aluminum occurs, resulting in the formation of an α-Al 2O3 layer. Additions of more than 0.3 wt.% yttrium result in preferential grain boundary oxidation and a convoluted alloy-oxide interface. This effect, “key-on effect” along with the formation of an aluminum and yttrium double oxide, produces increased oxide adherence for these alloys.

Method of preparing metal alloy coated composite powders

Abstract: Composite alloy coated particles are produced by blending finely divided metal coated composite particles, such as nickel coated graphite or cobalt coated tungsten carbide, with finely divided particles of at least one alloying metal, such as chromium or aluminum. The powder blend is heated in a protective atmosphere at a temperature and for a time sufficient to cause the alloying metal to alloy with the metal coatings of the composite powder particles without extensive sintering of the powder particles.

Spontaneous alloying of a gold substrate with lead monolayers

Abstract: Auger electron spectroscopy and low energy electron diffraction have been used to study monolayers of lead deposited in ultrahigh vacuum on to the (100) face of gold. There form first simple overlayer structures leading to a dense compact monolayer arrangement. Evidence is then found for the formation of an alloy layer which appears spontaneously at room temperature after completion of the first dense monolayer. The proposed alloy structure has the composition AuPb3.

Delta Ferrite and Martensite Formation in Stainless Steels From studies of 70 chill-cast stainless steel alloy types, nickel- and chromium-equivalents of 13 elements are evaluated for use in a revised Schaeffler diagram

Abstract: The effects of composi­ tion on delta ferrite and martensite formation were studied in chill-cast experimental stainless steel alloys. Nickel content was varied in each of seventy different alloy types to pro­ duce structures ranging from fully stable austenite to ones containing high percentages of delta ferrite or martensite. The nickel or chromium equivalents of Mn, Mo, Si, V, W, Ti, Cb, Ta, Al, C, N, Co and Cu were evaluated by regression analyses.